1. Field of the Invention
The present invention relates to a thin-film transistor liquid crystal display (TFT-LCD), and more particularly, to a liquid crystal display with a capacitance-compensated structure.
2. Description of the Prior Art
Due to the overlay shift between the pixel electrodes and the data lines caused by process variations, a parasitic capacitance (Cpd, Cpd′) is produced and causes a cross-talk phenomenon, as shown in FIG. 1. Additionally, the shot mura issue produced by the exposure process will also affect the picture quality. These are the major factors limiting the design of the aperture ratio.
There are many ways to decrease the parasitic capacitance and increase the aperture ratio. For example, a shielding capacitor and a polymer insulation film can be added between the data line and the pixel electrode to decrease the parasitic capacitance. As a result, the pixel electrode is able to overlap the data line thereby achieving a high aperture ratio. The primary factor influencing the reduction of the parasitic capacitance is related to the dielectric constant and the film thickness (i.e., the distance between the pixel electrode and the data line) of the polymer insulation film. However, as stated, influencing the reduction of parasitic capacitance is related to and limited by the development of polymer insulation film material. The dielectric constant of the polymer insulation film and the film thickness are possibly changed due to the other process steps, and thus influence the parasitic capacitance. Therefore, the overlap between the pixel electrode and the data line remain the cause of the unbalance of the parasitic capacitance as well as cross-talk and other defects.
In order to eliminate the parasitic capacitance effect, driving principles including dot inversion and column inversion (i.e., the polarity of two neighboring data line signals are opposite at the same time) are used to cancel the Cpd and Cpd′. Moreover, the ΔCpd will be minimized if the overlap areas between the pixel electrode and the data lines are the same.
The overlap area can be fixed when designing the photo mask as shown in FIG. 2. However, the original design value can be varied due to the overlay shift in the manufacturing process. The overlap areas between the pixel electrodes and the data lines will be changed and cause the parasitic capacitance unbalance as shown in FIG. 3.